RF transceiver having adaptive modulation

ABSTRACT

A modulation control module for use in an RF transceiver, the modulation control module includes a processing module and memory. The memory is operably coupled to the processing module, wherein the memory stores operational instructions that causes the processing module to: receive a multiple path channel estimation; and determining, for each transmit path of a multiple input multiple output (MIMO) wireless communication, a modulation control signal based on a corresponding portion of the multiple path channel estimation.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present U.S. Utility patent application claims priority pursuant to35 U.S.C. §120, as a continuation, to U.S. Utility patent applicationSer. No. 11/168,590, entitled “RF Transceiver Having AdaptiveModulation”, filed Jun. 28, 2005, pending, which is hereby incorporatedherein by reference in its entirety and made part of the present U.S.Utility patent application for all purposes.

U.S. Utility application Ser. No. 11/168,590, entitled “RF TransceiverHaving Adaptive Modulation”, filed Jun. 28, 2005, claims prioritypursuant to 35 USC §119(e) to U.S. Provisional Patent Application Ser.No. 60/673,451, entitled “Reduced Feedback For Beamforming in a WirelessCommunication”, filed Apr. 21, 2005, which is hereby incorporated hereinby reference in its entirety and made part of the present U.S. Utilitypatent application for all purposes.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

This invention relates generally to wireless communication systems andmore particularly to adaptive modulation for multiple input multipleoutput (MIMO) wireless communications.

2. Description of Related Art

Communication systems are known to support wireless and wire linedcommunications between wireless and/or wire lined communication devices.Such communication systems range from national and/or internationalcellular telephone systems to the Internet to point-to-point in-homewireless networks. Each type of communication system is constructed, andhence operates, in accordance with one or more communication standards.For instance, wireless communication systems may operate in accordancewith one or more standards including, but not limited to, IEEE 802.11,Bluetooth, advanced mobile phone services (AMPS), digital AMPS, globalsystem for mobile communications (GSM), code division multiple access(CDMA), local multi-point distribution systems (LMDS),multi-channel-multi-point distribution systems (MMDS), and/or variationsthereof.

Depending on the type of wireless communication system, a wirelesscommunication device, such as a cellular telephone, two-way radio,personal digital assistant (PDA), personal computer (PC), laptopcomputer, home entertainment equipment, et cetera communicates directlyor indirectly with other wireless communication devices. For directcommunications (also known as point-to-point communications), theparticipating wireless communication devices tune their receivers andtransmitters to the same channel or channels (e.g., one of the pluralityof radio frequency (RF) carriers of the wireless communication system)and communicate over that channel(s). For indirect wirelesscommunications, each wireless communication device communicates directlywith an associated base station (e.g., for cellular services) and/or anassociated access point (e.g., for an in-home or in-building wirelessnetwork) via an assigned channel. To complete a communication connectionbetween the wireless communication devices, the associated base stationsand/or associated access points communicate with each other directly,via a system controller, via the public switch telephone network, viathe Internet, and/or via some other wide area network.

For each wireless communication device to participate in wirelesscommunications, it includes a built-in radio transceiver (i.e., receiverand transmitter) or is coupled to an associated radio transceiver (e.g.,a station for in-home and/or in-building wireless communicationnetworks, RF modem, etc.). As is known, the receiver is coupled to theantenna and includes a low noise amplifier, one or more intermediatefrequency stages, a filtering stage, and a data recovery stage. The lownoise amplifier receives inbound RF signals via the antenna andamplifies then. The one or more intermediate frequency stages mix theamplified RF signals with one or more local oscillations to convert theamplified RF signal into baseband signals or intermediate frequency (IF)signals. The filtering stage filters the baseband signals or the IFsignals to attenuate unwanted out of band signals to produce filteredsignals. The data recovery stage recovers raw data from the filteredsignals in accordance with the particular wireless communicationstandard.

As is also known, the transmitter includes a data modulation stage, oneor more intermediate frequency stages, and a power amplifier. The datamodulation stage converts raw data into baseband signals in accordancewith a particular wireless communication standard. The one or moreintermediate frequency stages mix the baseband signals with one or morelocal oscillations to produce RF signals. The power amplifier amplifiesthe RF signals prior to transmission via an antenna.

In many systems, the transmitter will include one antenna fortransmitting the RF signals, which are received by a single antenna, ormultiple antennas, of a receiver. When the receiver includes two or moreantennas, the receiver will select one of them to receive the incomingRF signals. In this instance, the wireless communication between thetransmitter and receiver is a single-output-single-input (SISO)communication, even if the receiver includes multiple antennas that areused as diversity antennas (i.e., selecting one of them to receive theincoming RF signals). For SISO wireless communications, a transceiverincludes one transmitter and one receiver. Currently, most wirelesslocal area networks (WLAN) that are IEEE 802.11, 802.11a, 802.11b, or802.11g employ SISO wireless communications.

Other types of wireless communications includesingle-input-multiple-output (SIMO), multiple-input-single-output(MISO), and multiple-input-multiple-output (MIMO). In a SIMO wirelesscommunication, a single transmitter processes data into radio frequencysignals that are transmitted to a receiver. The receiver includes two ormore antennas and two or more receiver paths. Each of the antennasreceives the RF signals and provides them to a corresponding receiverpath (e.g., LNA, down conversion module, filters, and ADCs). Each of thereceiver paths processes the received RF signals to produce digitalsignals, which are combined and then processed to recapture thetransmitted data.

For a multiple-input-single-output (MISO) wireless communication, thetransmitter includes two or more transmission paths (e.g., digital toanalog converter, filters, up-conversion module, and a power amplifier)that each converts a corresponding portion of baseband signals into RFsignals, which are transmitted via corresponding antennas to a receiver.The receiver includes a single receiver path that receives the multipleRF signals from the transmitter.

For a multiple-input-multiple-output (MIMO) wireless communication, thetransmitter and receiver each include multiple paths. In such acommunication, the transmitter parallel processes data using a spatialand time encoding function to produce two or more streams of data. Thetransmitter includes multiple transmission paths to convert each streamof data into multiple RF signals. The receiver receives the multiple RFsignals via multiple receiver paths that recapture the streams of datautilizing a spatial and time decoding function. The recaptured streamsof data are combined and subsequently processed to recover the originaldata.

To further improve wireless communications, transceivers may incorporatebeamforming. In general, beamforming is a processing technique to createa focused antenna beam by shifting a signal in time or in phase toprovide gain of the signal in a desired direction and to attenuate thesignal in other directions. In order for a transmitter to properlyimplement beamforming, it needs to know properties of the channel overwhich the wireless communication is conveyed. Accordingly, the receivermust provide feedback information for the transmitter to determine theproperties of the channel. The feedback information may be sent as areceiver determined beamforming matrix (V) if a singular valuedecomposition can be determined or it may be sent as a channel matrix(H). Prior art papers (1) Digital beamforming basics (antennas) bySteyskal, Hans, Journal of Electronic Defense, Jul. 1, 1996; (2)Utilizing Digital Downconverters for Efficient Digital Beamforming, byClint Schreiner, Red River Engineering, no publication date; and (3)Interpolation Based Transmit Beamforming for MIMO-OFMD with PartialFeedback, by Jihoon Choi and Robert W. Heath, University of Texas,Department of Electrical and Computer Engineering, Wireless Networkingand Communications Group, Sep. 13, 2003.

The transmitter receives the estimated channel matrix (H) or thereceiver determined beamforming matrix (V) as feedback to adjust thetransmit beamforming processing. However, such information is not usedto optimize data throughput by adjusting the per channel and/or persubcarrier modulation scheme.

Therefore, a need exists for a method and apparatus that optimizes datathroughput of a MIMO and/or MISO wireless communication by adjusting theper channel and/or per subcarrier modulation scheme and to adjust acorresponding demodulation scheme.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to apparatus and methods of operationthat are further described in the following Brief Description of theDrawings, the Detailed Description of the Invention, and the claims.Other features and advantages of the present invention will becomeapparent from the following detailed description of the invention madewith reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic block diagram of a wireless communication systemin accordance with the present invention;

FIG. 2 is a schematic block diagram of a wireless communication devicein accordance with the present invention;

FIG. 3 is a schematic block diagram of another wireless communicationdevice in accordance with the present invention;

FIG. 4 is a schematic block diagram of baseband transmit processing inaccordance with the present invention;

FIG. 5 is a schematic block diagram of baseband receive processing inaccordance with the present invention;

FIG. 6 is a schematic block diagram of a beamforming wirelesscommunication in accordance with the present invention; and

FIG. 7 is a diagram of adaptive modulation of a wireless communicationin accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic block diagram illustrating a communication system10 that includes a plurality of base stations and/or access points 12,16, a plurality of wireless communication devices 18-32 and a networkhardware component 34. Note that the network hardware 34, which may be arouter, switch, bridge, modem, system controller, et cetera provides awide area network connection 42 for the communication system 10. Furthernote that the wireless communication devices 18-32 may be laptop hostcomputers 18 and 26, personal digital assistant hosts 20 and 30,personal computer hosts 24 and 32 and/or cellular telephone hosts 22 and28. The details of the wireless communication devices will be describedin greater detail with reference to FIGS. 2 and/or 3.

Wireless communication devices 22, 23, and 24 are located within anindependent basic service set (IBSS) area and communicate directly(i.e., point to point). In this configuration, these devices 22, 23, and24 may only communicate with each other. To communicate with otherwireless communication devices within the system 10 or to communicateoutside of the system 10, the devices 22, 23, and/or 24 need toaffiliate with one of the base stations or access points 12 or 16.

The base stations or access points 12, 16 are located within basicservice set (BSS) areas 11 and 13, respectively, and are operablycoupled to the network hardware 34 via local area network connections36, 38. Such a connection provides the base station or access point 1216 with connectivity to other devices within the system 10 and providesconnectivity to other networks via the WAN connection 42. To communicatewith the wireless communication devices within its BSS 11 or 13, each ofthe base stations or access points 12-16 has an associated antenna orantenna array. For instance, base station or access point 12 wirelesslycommunicates with wireless communication devices 18 and 20 while basestation or access point 16 wirelessly communicates with wirelesscommunication devices 26-32. Typically, the wireless communicationdevices register with a particular base station or access point 12, 16to receive services from the communication system 10.

Typically, base stations are used for cellular telephone systems andlike-type systems, while access points are used for in-home orin-building wireless networks (e.g., IEEE 802.11 and versions thereof,Bluetooth, and/or any other type of radio frequency based networkprotocol). Regardless of the particular type of communication system,each wireless communication device includes a built-in radio and/or iscoupled to a radio.

FIG. 2 is a schematic block diagram illustrating a wirelesscommunication device that includes the host device 18-32 and anassociated radio 60. For cellular telephone hosts, the radio 60 is abuilt-in component. For personal digital assistants hosts, laptop hosts,and/or personal computer hosts, the radio 60 may be built-in or anexternally coupled component.

As illustrated, the host device 18-32 includes a processing module 50,memory 52, a radio interface 54, an input interface 58, and an outputinterface 56. The processing module 50 and memory 52 execute thecorresponding instructions that are typically done by the host device.For example, for a cellular telephone host device, the processing module50 performs the corresponding communication functions in accordance witha particular cellular telephone standard.

The radio interface 54 allows data to be received from and sent to theradio 60. For data received from the radio 60 (e.g., inbound data), theradio interface 54 provides the data to the processing module 50 forfurther processing and/or routing to the output interface 56. The outputinterface 56 provides connectivity to an output display device such as adisplay, monitor, speakers, et cetera such that the received data may bedisplayed. The radio interface 54 also provides data from the processingmodule 50 to the radio 60. The processing module 50 may receive theoutbound data from an input device such as a keyboard, keypad,microphone, et cetera via the input interface 58 or generate the dataitself. For data received via the input interface 58, the processingmodule 50 may perform a corresponding host function on the data and/orroute it to the radio 60 via the radio interface 54.

Radio 60 includes a host interface 62, digital receiver processingmodule 64, an analog-to-digital converter 66, a high pass and low passfilter module 68, an IF mixing down conversion stage 70, a receiverfilter 71, a low noise amplifier 72, a transmitter/receiver switch 73, alocal oscillation module 74, memory 75, a digital transmitter processingmodule 76, a digital-to-analog converter 78, a filtering/gain module 80,an IF mixing up conversion stage 82, a power amplifier 84, a transmitterfilter module 85, a channel bandwidth adjust module 87, and an antenna86. The antenna 86 may be a single antenna that is shared by thetransmit and receive paths as regulated by the Tx/Rx switch 73, or mayinclude separate antennas for the transmit path and receive path. Theantenna implementation will depend on the particular standard to whichthe wireless communication device is compliant.

The digital receiver processing module 64 and the digital transmitterprocessing module 76, in combination with operational instructionsstored in memory 75, execute digital receiver functions and digitaltransmitter functions, respectively. The digital receiver functionsinclude, but are not limited to, digital intermediate frequency tobaseband conversion, demodulation, constellation demapping, decoding,and/or descrambling. The digital transmitter functions include, but arenot limited to, scrambling, encoding, constellation mapping, modulation,and/or digital baseband to IF conversion. The digital receiver andtransmitter processing modules 64 and 76 may be implemented using ashared processing device, individual processing devices, or a pluralityof processing devices. Such a processing device may be a microprocessor,micro-controller, digital signal processor, microcomputer, centralprocessing unit, field programmable gate array, programmable logicdevice, state machine, logic circuitry, analog circuitry, digitalcircuitry, and/or any device that manipulates signals (analog and/ordigital) based on operational instructions. The memory 75 may be asingle memory device or a plurality of memory devices. Such a memorydevice may be a read-only memory, random access memory, volatile memory,non-volatile memory, static memory, dynamic memory, flash memory, and/orany device that stores digital information. Note that when theprocessing module 64 and/or 76 implements one or more of its functionsvia a state machine, analog circuitry, digital circuitry, and/or logiccircuitry, the memory storing the corresponding operational instructionsis embedded with the circuitry comprising the state machine, analogcircuitry, digital circuitry, and/or logic circuitry.

In operation, the radio 60 receives outbound data 94 from the hostdevice via the host interface 62. The host interface 62 routes theoutbound data 94 to the digital transmitter processing module 76, whichprocesses the outbound data 94 in accordance with a particular wirelesscommunication standard (e.g., IEEE 802.11, Bluetooth, et cetera) toproduce outbound baseband signals 96. The outbound baseband signals 96will be digital base-band signals (e.g., have a zero IF) or a digitallow IF signals, where the low IF typically will be in the frequencyrange of one hundred kilohertz to a few megahertz.

The digital-to-analog converter 78 converts the outbound basebandsignals 96 from the digital domain to the analog domain. Thefiltering/gain module 80 filters and/or adjusts the gain of the analogsignals prior to providing it to the IF mixing stage 82. The IF mixingstage 82 converts the analog baseband or low IF signals into RF signalsbased on a transmitter local oscillation 83 provided by localoscillation module 74. The power amplifier 84 amplifies the RF signalsto produce outbound RF signals 98, which are filtered by the transmitterfilter module 85. The antenna 86 transmits the outbound RF signals 98 toa targeted device such as a base station, an access point and/or anotherwireless communication device.

The radio 60 also receives inbound RF signals 88 via the antenna 86,which were transmitted by a base station, an access point, or anotherwireless communication device. The antenna 86 provides the inbound RFsignals 88 to the receiver filter module 71 via the Tx/Rx switch 73,where the Rx filter 71 bandpass filters the inbound RF signals 88. TheRx filter 71 provides the filtered RF signals to low noise amplifier 72,which amplifies the signals 88 to produce an amplified inbound RFsignals. The low noise amplifier 72 provides the amplified inbound RFsignals to the IF mixing module 70, which directly converts theamplified inbound RF signals into an inbound low IF signals or basebandsignals based on a receiver local oscillation 81 provided by localoscillation module 74. The down conversion module 70 provides theinbound low IF signals or baseband signals to the filtering/gain module68. The high pass and low pass filter module 68 filters, based onsettings provided by the channel bandwidth adjust module 87, the inboundlow IF signals or the inbound baseband signals to produce filteredinbound signals.

The analog-to-digital converter 66 converts the filtered inbound signalsfrom the analog domain to the digital domain to produce inbound basebandsignals 90, where the inbound baseband signals 90 will be digitalbase-band signals or digital low IF signals, where the low IF typicallywill be in the frequency range of one hundred kilohertz to a fewmegahertz. The digital receiver processing module 64, based on settingsprovided by the channel bandwidth adjust module 87, decodes,descrambles, demaps, and/or demodulates the inbound baseband signals 90to recapture inbound data 92 in accordance with the particular wirelesscommunication standard being implemented by radio 60. The host interface62 provides the recaptured inbound data 92 to the host device 18-32 viathe radio interface 54.

As one of average skill in the art will appreciate, the wirelesscommunication device of FIG. 2 may be implemented using one or moreintegrated circuits. For example, the host device may be implemented onone integrated circuit, the digital receiver processing module 64, thedigital transmitter processing module 76 and memory 75 may beimplemented on a second integrated circuit, and the remaining componentsof the radio 60, less the antenna 86, may be implemented on a thirdintegrated circuit. As an alternate example, the radio 60 may beimplemented on a single integrated circuit. As yet another example, theprocessing module 50 of the host device and the digital receiver andtransmitter processing modules 64 and 76 may be a common processingdevice implemented on a single integrated circuit. Further, the memory52 and memory 75 may be implemented on a single integrated circuitand/or on the same integrated circuit as the common processing modulesof processing module 50 and the digital receiver and transmitterprocessing module 64 and 76.

FIG. 3 is a schematic block diagram illustrating a wirelesscommunication device that includes the host device 18-32 and anassociated radio 60. For cellular telephone hosts, the radio 60 is abuilt-in component. For personal digital assistants hosts, laptop hosts,and/or personal computer hosts, the radio 60 may be built-in or anexternally coupled component.

As illustrated, the host device 18-32 includes a processing module 50,memory 52, radio interface 54, input interface 58 and output interface56. The processing module 50 and memory 52 execute the correspondinginstructions that are typically done by the host device. For example,for a cellular telephone host device, the processing module 50 performsthe corresponding communication functions in accordance with aparticular cellular telephone standard.

The radio interface 54 allows data to be received from and sent to theradio 60. For data received from the radio 60 (e.g., inbound data), theradio interface 54 provides the data to the processing module 50 forfurther processing and/or routing to the output interface 56. The outputinterface 56 provides connectivity to an output display device such as adisplay, monitor, speakers, et cetera such that the received data may bedisplayed. The radio interface 54 also provides data from the processingmodule 50 to the radio 60. The processing module 50 may receive theoutbound data from an input device such as a keyboard, keypad,microphone, et cetera via the input interface 58 or generate the dataitself. For data received via the input interface 58, the processingmodule 50 may perform a corresponding host function on the data and/orroute it to the radio 60 via the radio interface 54.

Radio 60 includes a host interface 62, a baseband processing module 100,memory 65, a plurality of radio frequency (RF) transmitters 106-110, atransmit/receive (T/R) module 114, a plurality of antennas 81-85, aplurality of RF receivers 118-120, a channel bandwidth adjust module 87,and a local oscillation module 74. The baseband processing module 100,in combination with operational instructions stored in memory 65,executes digital receiver functions and digital transmitter functions,respectively. The digital receiver functions include, but are notlimited to, digital intermediate frequency to baseband conversion,demodulation, constellation demapping, decoding, de-interleaving, fastFourier transform, cyclic prefix removal, space and time decoding,and/or descrambling. The digital transmitter functions include, but arenot limited to, scrambling, encoding, interleaving, constellationmapping, modulation, inverse fast Fourier transform, cyclic prefixaddition, space and time encoding, and digital baseband to IFconversion. The baseband processing modules 100 may be implemented usingone or more processing devices. Such a processing device may be amicroprocessor, micro-controller, digital signal processor,microcomputer, central processing unit, field programmable gate array,programmable logic device, state machine, logic circuitry, analogcircuitry, digital circuitry, and/or any device that manipulates signals(analog and/or digital) based on operational instructions. The memory 65may be a single memory device or a plurality of memory devices. Such amemory device may be a read-only memory, random access memory, volatilememory, non-volatile memory, static memory, dynamic memory, flashmemory, and/or any device that stores digital information. Note thatwhen the processing module 100 implements one or more of its functionsvia a state machine, analog circuitry, digital circuitry, and/or logiccircuitry, the memory storing the corresponding operational instructionsis embedded with the circuitry comprising the state machine, analogcircuitry, digital circuitry, and/or logic circuitry.

In operation, the radio 60 receives outbound data 94 from the hostdevice via the host interface 62. The baseband processing module 64receives the outbound data 88 and, based on a mode selection signal 102,produces one or more outbound symbol streams 90. The mode selectionsignal 102 will indicate a particular mode of operation that iscompliant with one or more specific modes of the various IEEE 802.11standards. For example, the mode selection signal 102 may indicate afrequency band of 2.4 GHz, a channel bandwidth of 20 or 22 MHz and amaximum bit rate of 54 megabits-per-second. In this general category,the mode selection signal will further indicate a particular rateranging from 1 megabit-per-second to 54 megabits-per-second. Inaddition, the mode selection signal will indicate a particular type ofmodulation, which includes, but is not limited to, Barker CodeModulation, BPSK, QPSK, CCK, 16 QAM, 64 QAM and/or 256 QAM. The modeselect signal 102 may also include a code rate, a number of coded bitsper subcarrier (NBPSC), coded bits per OFDM symbol (NCBPS), and/or databits per OFDM symbol (NDBPS). The mode selection signal 102 may alsoindicate a particular channelization for the corresponding mode thatprovides a channel number and corresponding center frequency. The modeselect signal 102 may further indicate a power spectral density maskvalue and a number of antennas to be initially used for a MIMOcommunication.

The baseband processing module 100, based on the mode selection signal102 produces one or more outbound symbol streams 104 from the outbounddata 94. For example, if the mode selection signal 102 indicates that asingle transmit antenna is being utilized for the particular mode thathas been selected, the baseband processing module 100 will produce asingle outbound symbol stream 104. Alternatively, if the mode selectsignal 102 indicates 2, 3 or 4 antennas, the baseband processing module100 will produce 2, 3 or 4 outbound symbol streams 104 from the outbounddata 94.

Depending on the number of outbound streams 104 produced by the basebandmodule 10, a corresponding number of the RF transmitters 106-110 will beenabled to convert the outbound symbol streams 104 into outbound RFsignals 112. In general, each of the RF transmitters 106-110 includes adigital filter and upsampling module, a digital to analog conversionmodule, an analog filter module, a frequency up conversion module, apower amplifier, and a radio frequency bandpass filter. The RFtransmitters 106-110 provide the outbound RF signals 112 to thetransmit/receive module 114, which provides each outbound RF signal to acorresponding antenna 81-85.

When the radio 60 is in the receive mode, the transmit/receive module114 receives one or more inbound RF signals 116 via the antennas 81-85and provides them to one or more RF receivers 118-122, which will bedescribed in greater detail with reference to FIG. 4. The RF receiver118-122, based on settings provided by the channel bandwidth adjustmodule 87, converts the inbound RF signals 116 into a correspondingnumber of inbound symbol streams 124. The number of inbound symbolstreams 124 will correspond to the particular mode in which the data wasreceived. The baseband processing module 100 converts the inbound symbolstreams 124 into inbound data 92, which is provided to the host device18-32 via the host interface 62.

As one of average skill in the art will appreciate, the wirelesscommunication device of FIG. 3 may be implemented using one or moreintegrated circuits. For example, the host device may be implemented onone integrated circuit, the baseband processing module 100 and memory 65may be implemented on a second integrated circuit, and the remainingcomponents of the radio 60, less the antennas 81-85, may be implementedon a third integrated circuit. As an alternate example, the radio 60 maybe implemented on a single integrated circuit. As yet another example,the processing module 50 of the host device and the baseband processingmodule 100 may be a common processing device implemented on a singleintegrated circuit. Further, the memory 52 and memory 65 may beimplemented on a single integrated circuit and/or on the same integratedcircuit as the common processing modules of processing module 50 and thebaseband processing module 100.

FIG. 4 is a schematic block diagram of baseband transmit processing100-TK within the baseband processing module 100, which includes anencoding module 121, a puncture module 123, an interleaving module 125,a plurality of symbol mapping modules 128, 130, a beamforming module (V)132, a modulation control module 135, and a plurality of inverse fastFourier transform (IFFT) modules 134, 136 for converting the outbounddata 94 into the outbound symbol stream 104. In one embodiment, theinterleaving module 125 includes a switching module and a plurality ofinterleavers 127, 126. As one of ordinary skill in the art willappreciate, the baseband transmit processing 100-TK may include two ormore of each of the interleavers 127, 126, the symbol mapping modules128, 130, and the IFFT modules 134, 136, wherein the number of eachmodule corresponds to the number of transmit paths of a MIMO wirelesscommunication. In addition, one of ordinary skill in art will furtherappreciate that the encoding module 121, puncture module 123, theinterleavers modules 127, 126, the symbol mapping modules 128, 130, andthe IFFT modules 134, 136 may be function in accordance with one or morewireless communication standards including, but not limited to, IEEE802.11a, b, g, n.

In one embodiment, the encoding module 121 is operably coupled toconvert outbound data 94 into encoded data in accordance with one ormore wireless communication standards. The puncture module 123 puncturesthe encoded data to produce punctured encoded data. The plurality ofinterleavers 127, 126 is operably coupled to interleave the puncturedencoded data into a plurality of interleaved streams of data. Theplurality of symbol mapping modules 128, 130 is operably coupled to mapthe plurality of interleaved streams of data into a plurality of streamsof data symbols based on a plurality of modulation control signals 139provided by the modulation module 135. The beamforming module 132 isoperably coupled to beamform, using a unitary matrix having polarcoordinates, the plurality of streams of data symbols into a pluralityof streams of beamformed symbols. The plurality of IFFT modules 124, 136is operably coupled to convert the plurality of streams of beamformedsymbols into a plurality of outbound symbol streams.

The beamforming module 132 is operably coupled to multiply a beamformingunitary matrix (V) with baseband signals provided by the plurality ofconstellation mapping modules 128, 130. The beamforming unitary matrix Vused by the beamforming module 132 satisfies the conditions of“V*V=VV*=“I”, where “I” is an identity matrix of [1 0; 0 1] for 2×2 MIMOwireless communication, is [1 0 0; 0 1 0; 0 0 1] for 3×3 MIMO wirelesscommunication, or is [1 0 0 0; 0 1 0 0; 0 0 1 0; 0 0 0 1] for 4×4 MIMOwireless communication. In this equation, V*V means “conjugate (V) timesV” and VV* means “V times conjugate (V)”. Note that V may be a 2×2unitary matrix for a 2×2 MIMO wireless communication, a 3×3 unitarymatrix for a 3×3 MIMO wireless communication, and a 4×4 unitary matrixfor a 4×4 MIMO wireless communication. Further note that for each columnof V, a first row of polar coordinates including real values asreferences and a second row of polar coordinates including phase shiftvalues.

In one embodiment, the symbol mapping modules 128, 130 function inaccordance with one of the IEEE 802.11x standards to provide an OFDM(Orthogonal Frequency Domain Multiplexing) frequency domain basebandsignals that includes a plurality of tones, or subcarriers, for carryingdata. Each of the data carrying tones represents a symbol mapped to apoint on a modulation dependent constellation map. For instance, a 16QAM (Quadrature Amplitude Modulation) includes 16 constellation points,each corresponding to a different symbol. The particular modulationscheme used on a per transmit path basis, on a per subcarrier basis,and/or a combination thereof is dictated by the modulation controlmodule 135 via the modulation control modules. For example, if themodulation scheme is adjusted on a per transmit path basis, themodulation control module 135 may determine that one transmit path willuse a 16 QAM modulation scheme, while another may use a 64 QAMmodulation scheme, and yet another transmit path may use a QPSKmodulation scheme. As another example, if the modulation scheme isadjusted on a per subcarrier basis, each sub carrier of each transmitpath may have a different modulation scheme. For instance, somesubcarriers may have a 16 QAM modulation scheme, while others may use a64 QAM modulation scheme, and some others may use a QPSK modulationscheme.

The modulation control module 135 determines the modulation controlsignals 139 based on a multiple path channel estimate 137. In oneembodiment, the modulation control module 135 receiving the multiplepath channel estimation 137 from another RF transceiver. From this, themodulation control module 135 determines, for each of the plurality ofsymbol mapping modules, a corresponding one of the plurality ofmodulation control signals based on a corresponding portion of themultiple path channel estimation. For instance, the modulation controlmodule 135 may receive the multiple path channel estimation 137 as adiagonalized channel (H) based on eigen beamforming using singular valuedecomposition, wherein H=UDV*, such that y=Hx+n=UDV*x+n, where Ucorresponds to the unitary de-beamforming matrix, V corresponds to theunitary beamforming matrix, V* corresponds to a conjugate of the unitarybeamforming matrix, y corresponds to the plurality of streams offrequency domain inbound baseband symbols, x corresponds to theplurality of streams of symbols, and n corresponds to noise.

For a diagonalized channel (H), the modulation control module maydetermine the corresponding modulation control signals for a 2×Nmultiple input multiple output (MIMO) wireless communication by firstsetting z=Vx, where V corresponds to the unitary beamforming matrix andx corresponds to the plurality of streams of symbols. The modulationcontrol module 135 then determines a conjugate of the unitaryde-beamforming matrix multiplied by the plurality of streams offrequency domain inbound baseband symbols such thatU*y=U*UDV*Vz+U*n=Dz+N, where D corresponds to a diagonal matrix of D=[s₁0;0 s₂] and N corresponds to a noise power, and where s₁ and s₂represent first and second signal components. In various embodiments, s₁and s₂ represent first and second signal components, where a signalcomponent may be a signal representation of a subcarrier of a transmitpath, and/or a signal representation of the transmit path.

The modulation control module 135 then determines signal to noise ratio(SNR) for each transmit path of the MIMO wireless communication, whereSNR₁=s₁ ²/N₀, and SNR₂=s₂ ²/N₀, where the SNR₁ represents the SNR for afirst transmit path of the MIMO wireless communication and the SNR₂represents the SNR for a second transmit path of the MIMO wirelesscommunication. The modulation control module 135 then determines thecorresponding modulated control signals based on at least one of theSNR₁ and the SNR₂. For example, for a first transmit path, if the SNR isbetween a first and second threshold (e.g., between 75 dB and 90 dB) amodulation scheme of 64 QAM may be used and, for a second transmit path,if the SNR is between a different set of thresholds (e.g., 60 dB and 74dB), a modulation scheme of 16 QAM may be used. As a further example,the modulation control module 135 may determine the SNR for subcarriersof each transmit path and determine the modulation scheme for eachsubcarrier based on the SNR.

As another example, the modulation control module 135 may determine thecorresponding modulated control signals by first determining a geometricmean for the SNR (SNRgeo) for each of the transmit paths of the MIMOwireless communication over subcarriers of an OFDM (orthogonal frequencydivision multiplex) frame of the MIMO wireless communication, whereSNRgeo=prod(1+SNRi)^((1/(N-1))). The modulation control module 135 thendetermines assigned bits (b) for the each of the transmit paths based onan Aslanis formula, where b=log₂(1+SNR/G), where G corresponds to marginsuch that b₁<=log₂(1+SNRgeo₁/G₁) and b₂<=log₂(1+SNRgeo₂/G₂). Themodulation control module 135 then relates, or corresponds, the assignedbits for the each of the transmit paths to a modulation convention toproduce the corresponding one of the plurality of modulation controlsignals.

As an extension of the preceding example, the modulation control module135 may perform the corresponding of the assigned bits for the each ofthe transmit paths to a modulation convention by first limiting one ofthe assigned bits in accordance withb_(i)=floor(log₂(1+SNRgeo_(i)/G_(i))/2)*2 such that a maximum b_(i)includes 8 bits/tone/stream. The modulation control module 135 then setsa margin (G) to 0 dB. The modulation control module 135 then equatesassigned bits b_(i) of 2 to a 4QAM (quadrature amplitude modulation)modulation convention, assigned bits b_(i) of 4 to a 16 QAM modulationconvention, assigned bits b_(i) of 6 to a 64 QAM modulation convention,and assigned bits b_(i) of 8 to a 256 QAM modulation convention.

In one embodiment, the modulation control module 135 generates themodulation control signals as part of the mode select signal 102 toinclude, but not limited to, a code rate, a number of coded bits persubcarrier (NBPSC), coded bits per OFDM symbol (NCBPS), and/or data bitsper OFDM symbol (NDBPS).

FIG. 5 is a schematic block diagram of baseband receive processing100-RX that includes a plurality of fast Fourier transform (FFT) modules140, 142, a beamforming (U) module 144, an equalizing module 145, aplurality of demapping modules 146, 148, a deinterleaving module 155, adepuncture module 154, and a decoding module 156 for converting aplurality of inbound symbol streams 124 into inbound data 92. In oneembodiment, the deinterleaving module 155 includes a switching moduleand a plurality of de-interleavers 150, 152. As one of ordinary skill inthe art will appreciate, the baseband receive processing 100-RX mayinclude two or more of each of the deinterleavers 150, 152, thedemapping modules 146, 148, and the FFT modules 140, 142, where thenumber of each module corresponds to the number of receive paths (e.g.,receiver antennas) in a MIMO wireless communication. In addition, one ofordinary skill in art will further appreciate that the decoding module156, depuncture module 154, the deinterleavers 150, 152, the decodingmodules 146, 148, and the FFT modules 140, 142 may be function inaccordance with one or more wireless communication standards including,but not limited to, IEEE 802.11a, b, g, n.

In an embodiment, a plurality of FFT modules 140, 142 is operablycoupled to convert a plurality of inbound symbol streams 124 into aplurality of streams of frequency domain inbound symbols. Thede-beamforming module 144 is operably coupled to inverse beamform, usinga unitary matrix having polar coordinates, the plurality of streams ofbeamformed symbols into a plurality of streams of de-beamformed inboundsymbols. The equalizing module 145 is operably coupled to equalize theplurality of streams of de-beamformed inbound baseband symbols inaccordance with a channel estimation 147 to produce a plurality ofstreams of equalized de-beamformed inbound baseband symbols. The channelestimation 147 may be derived using one or more of a plurality of knownmethods for determining a channel response.

The plurality of demapping modules 146, 148 is operably coupled to demapplurality of streams of equalized de-beamformed inbound baseband symbolsin accordance with a plurality of demodulation signals 159 to produce aplurality of streams of inbound baseband signals. The deinterleaver 150,152 are operably coupled to deinterleave the plurality of inboundbaseband signals to produce demodulated inbound baseband signals. Thedecoding module 156 is operably coupled to convert the demodulatedinbound baseband signals into inbound data 92.

In an embodiment, the beamforming module 144 is operably coupled tomultiply a beamforming unitary matrix (U) with baseband signals providedby the plurality of FFT modules 140, 142. The beamforming unitary matrixU used by the beamforming module 144 satisfies the conditions of“U*U=UU=“I”, where “I” is an identity matrix of [1 0; 0 1] for 2×2 MIMOwireless communication, is [1 0 0; 0 1 0; 0 0 1] for 3×3 MIMO wirelesscommunication, or is [1 0 0 0; 0 1 0 0; 0 0 1 0; 0 0 0 1] for 4×4 MIMOwireless communication. In this equation, U*U means “conjugate (U) timesU” and UU* means “U times conjugate (U)”. Note that U may be a 2×2unitary matrix for a 2×2 MIMO wireless communication, a 3×3 unitarymatrix for a 3×3 MIMO wireless communication, and a 4×4 unitary matrixfor a 4×4 MIMO wireless communication. Further note that for each columnof U, a first row of polar coordinates including real values asreferences and a second row of polar coordinates including phase shiftvalues.

In an embodiment, the FFT modules 140, 142 function in accordance withone of the IEEE 802.11x standards to provide an OFDM (OrthogonalFrequency Domain Multiplexing) frequency domain baseband signals thatincludes a plurality of tones, or subcarriers, for carrying data. Eachof the data carrying tones represents a symbol mapped to a point on amodulation dependent constellation map.

The modulation control module 135 is operably coupled to generate thedemodulation control signals 159 based on a multiple channel pathestimation. In one embodiment, the modulation control module 135generates the plurality of demodulation control signals by interpretinga signal field of a frame received from another RF transceiver.

FIG. 6 is a schematic block diagram of a MIMO wireless communicationbetween a transmitting wireless communication device (TX) and areceiving wireless communication device (RX). In this illustration, theMIMO wireless communication is a M by N MIMO wireless communication(i.e., the transmitter includes M transmit antennas and N receiverantennas. The multiple path channel may be represented as a matrix (H),which is a function of the individual channel paths H1_1, H1_n, Hm_1,Hm_n. The receiver RX may calculate the multiple path channel matrix Hbased on the equation H=UDV*(H—represents the channel, U is the receiverde-beamforming unitary matrix, and V* is the conjugate of thetransmitter beamforming unitary matrix). With H=UDV*, y (the receivedsignal)=Hx+N, where x represents the transmitted signals and Nrepresents noise. If z=Vx, then U*y=U*UDV*Vz+U*n=Dz+N, where Dcorresponds to a diagonal matrix of D=[s₁ 0;0 s₂] and N corresponds to anoise power, and where s₁ and s₂ represent first and second signalcomponents. In various embodiments, s₁ and s₂ represent first and secondsignal components, where a signal component may be a signalrepresentation of a subcarrier of a transmit path, and/or a signalrepresentation of the transmit path.

Upon determining the multiple path channel matrix H and the conjugate ofthe transmitter beamforming unitary matrix V*, the receiver RX providesa feedback signal 160 to the transmitter TX. The feedback 160 may be thechannel matrix H and/or the conjugate of the transmitter beamformingunitary matrix V*. From either type of feedback, the transmitter TXdetermines the modulation and demodulation control signals.

FIG. 7 is a diagram illustrating a MIMO wireless communication. In thisillustration, a MIMO wireless communication begins when a transmittertransmits a training sequence 162 to a receiver. The training sequencemay be in accordance with one or more wireless communication standards(e.g., IEEE 802.11a, b, g, n, etc.). As the receiver is receiving thetraining sequence, it is calculating 164 the channel matrix H and mayalso be determining the conjugate of the transmitter beamforming unitarymatrix V*. Once the receiver has completed this calculation, ittransmits feedback 160 to the transmitter. The feedback 160 may be thechannel matrix H and/or the conjugate of the transmitter beamformingunitary matrix V*. Note that the feedback 160 may further include thediagonal matrix D.

Upon receiving the feedback, 160 the transmitter TX functions todetermine the modulation and demodulation control signals 166. This maybe done as previously discussed with reference to FIG. 4. Thetransmitter then generates a frame that includes a signal field 168 anda plurality of data fields 170. The signal field 168 includes thedemodulation control signals and the data fields 170 include data thathas been modulated in accordance with the modulation control signals.

As one of ordinary skill in the art will appreciate, the term“substantially” or “approximately”, as may be used herein, provides anindustry-accepted tolerance to its corresponding term and/or relativitybetween items. Such an industry-accepted tolerance ranges from less thanone percent to twenty percent and corresponds to, but is not limited to,component values, integrated circuit process variations, temperaturevariations, rise and fall times, and/or thermal noise. Such relativitybetween items ranges from a difference of a few percent to magnitudedifferences. As one of ordinary skill in the art will furtherappreciate, the term “operably coupled”, as may be used herein, includesdirect coupling and indirect coupling via another component, element,circuit, or module where, for indirect coupling, the interveningcomponent, element, circuit, or module does not modify the informationof a signal but may adjust its current level, voltage level, and/orpower level. As one of ordinary skill in the art will also appreciate,inferred coupling (i.e., where one element is coupled to another elementby inference) includes direct and indirect coupling between two elementsin the same manner as “operably coupled”. As one of ordinary skill inthe art will further appreciate, the term “compares favorably”, as maybe used herein, indicates that a comparison between two or moreelements, items, signals, etc., provides a desired relationship. Forexample, when the desired relationship is that signal 1 has a greatermagnitude than signal 2, a favorable comparison may be achieved when themagnitude of signal 1 is greater than that of signal 2 or when themagnitude of signal 2 is less than that of signal 1.

The preceding discussion has presented a method and apparatus foroptimizing data throughput of a MIMO wireless communication. As one ofaverage skill in the art will appreciate, other embodiments may bederived from the present teachings without deviating from the scope ofthe claims. For instance, adaptive modulations using SVD (singular valuedecomposition) enables the assigning of more bits on better space modechannels and less bits on worse space mode channels such that theprobability of wrong detection of signals is reduced, thereby increasingmargin. Note that in one embodiment, the first singular value is greaterthan the second singular value and, as such, the transmission throughthe first space mode is more reliable than through the second spacemode.

1. A radio frequency (RF) transceiver having adaptive modulation, the RFtransceiver comprises: an RF front-end operably coupled to convert aplurality of streams of outbound baseband signals into outbound RFsignals and to convert inbound RF signals into a plurality of streams ofinbound baseband signals; a baseband transmitter section including: anencoding module operably coupled to encode outbound data to produceencoded data; an interleaving module operably coupled to interleave theencoded data into a plurality of interleaved encoded data streams; aplurality of symbol mapping modules operably coupled to map, inaccordance with a plurality of modulation control signals, the pluralityof interleaved encoded data streams into a plurality of streams ofsymbols; a beamforming module operably coupled to multiply the pluralityof streams of symbols by a unitary beamforming matrix to produce aplurality of beamformed streams of symbols, wherein the unitarybeamforming matrix is determined based on a multiple path channelestimation from a receiver feedback signal from another RF transceiver;and a plurality of inverse fast Fourier transform modules operablycoupled to convert the plurality of beamformed streams of symbols from afrequency domain to a time domain to produce the plurality of streams ofoutbound baseband signals; and a modulation control module operablycoupled to produce the plurality of modulation control signals, whereinthe plurality of modulation control signals are determined based on themultiple path channel estimation from the receiver feedback signal fromthe another RF transceiver, wherein the modulation control modulefunctions to determine the plurality of modulation control signals by:determining a signal to noise ratio for each transmit path based on acorresponding portion of the multiple path channel estimation from thereceiver feedback signal; in response to the signal to noise ratiodetermined for each transmit path, determining a modulation scheme foreach transmit path; and producing the plurality of modulation controlsignals in response to the modulation scheme determined for eachtransmit path.
 2. The RF transceiver of claim 1, wherein the multiplepath channel estimation comprises: a diagonalized channel (H) based oneigen beamforming using singular value decomposition, wherein H=UDV*,such that y=Hx+n=UDV*x+n, where U corresponds to the unitaryde-beamforming matrix, V corresponds to the unitary beamforming matrix,V* corresponds to a conjugate of the unitary beamforming matrix, ycorresponds to the plurality of streams of frequency domain inboundbaseband symbols, x corresponds to the plurality of streams of symbols,and n corresponds to noise, D corresponds to a diagonal matrix of D=[s₁0;0 s₂].
 3. The RF transceiver of claim 2, wherein the determining, foreach of the plurality of symbol mapping modules, a corresponding one ofthe plurality of modulation control signals comprises for a 2×N multipleinput multiple output (MIMO) wireless communication: setting z=Vx;determining a conjugate of the unitary de-beamforming matrix multipliedby the plurality of streams of frequency domain inbound baseband symbolssuch that U*y=U*UDV*Vz+U*n=Dz+N, where D corresponds to a diagonalmatrix of D=[s₁ 0;0 s₂] and N corresponds to a noise power, and where s₁and s₂ represent first and second signal components; determining signalto noise ratio (SNR) for each transmit path of the MIMO wirelesscommunication, where SNR₁=S₁ ²/N₀, and SNR₂=S₂ ²/N₀; where the SNR₁represents the SNR for a first transmit path of the MIMO wirelesscommunication and the SNR₂ represents the SNR for a second transmit pathof the MIMO wireless communication; and determining the correspondingone of the plurality of modulated control signals based on at least oneof the SNR₁ and the SNR₂.
 4. The RF transceiver of claim 3, wherein thedetermining the corresponding one of the plurality of modulated controlsignals further comprises: determining a geometric mean for the SNR(SNRgeo) for each of the transmit paths of the MIMO wirelesscommunication over subcarriers of an OFDM (orthogonal frequency divisionmultiplex) frame of the MIMO wireless communication, whereSNRgeo=prod(1+SNRi)^(1/(N-1)); determining assigned bits (b) for theeach of the transmit paths based on an Aslanis formula, whereb=log₂(1+SNR/G), where G corresponds to margin such thatb₁<=log₂(1+SNRgeo₁/G₁) and b₂<=log₂(1+SNRgeo₂/G₂); and corresponding theassigned bits for the each of the transmit paths to a modulationconvention to produce the corresponding one of the plurality ofmodulation control signals.
 5. The RF transceiver of claim 4, whereinthe corresponding the assigned bits for the each of the transmit pathsto a modulation convention further comprises: limiting one of theassigned bits in accordance withb_(i)=floor(log₂(1+SNRgeo_(i)/G_(i))/2)*2 such that a maximum b_(i)includes 8 bits/tone/stream; setting margin (G) to 0 dB; and equating ab_(i) of 2 to a 4QAM (quadrature amplitude modulation) modulationconvention, a b_(i) of 4 to a 16 QAM modulation convention, a b_(i) of 6to a 64QAM modulation convention, and a b_(i) of 8 to a 256 QAMmodulation convention.
 6. The RF transceiver of claim 1, furthercomprising: a baseband receiver section including: a plurality of fastFourier transform modules operably coupled to convert a correspondingone of the plurality of streams of inbound baseband signals from a timedomain to a frequency domain to produce a plurality of streams offrequency domain inbound baseband symbols; a de-beamforming moduleoperably coupled to multiply the plurality of streams of frequencydomain inbound baseband symbols by a unitary de-beamforming matrix toproduce a plurality of streams of de-beamformed inbound basebandsymbols; an equalizing module operably coupled to equalize the pluralityof streams of de-beamformed inbound baseband symbols in accordance witha channel estimation to produce a plurality of streams of equalizedde-beamformed inbound baseband symbols; a plurality of de-mappingmodules operably coupled to demap the plurality of streams of equalizedde-beamformed inbound baseband symbols in accordance with a plurality ofdemodulation control signals to produce a plurality of streams ofinbound baseband signals; a deinterleaving module operably coupled todeinterleave the plurality of streams of inbound baseband signals toproduce demodulated inbound baseband signals; and decoding moduleoperably coupled to decode the demodulated inbound baseband signals fromeach of the plurality of baseband demodulating paths to produce inbounddata.
 7. A baseband transmit processing module, comprising: an encodingmodule operably coupled to encode outbound data to produce encoded data;an interleaving module operably coupled to interleave the encoded datainto a plurality of interleaved encoded data streams; a plurality ofsymbol mapping modules operably coupled to map, in accordance with aplurality of modulation control signals, the plurality of interleavedencoded data streams into a plurality of streams of symbols, whereineach of the plurality of modulation control signals indicates one of aplurality of modulation schemes; a beamforming module operably coupledto multiplying the plurality of streams of symbols by a beamformingmatrix to produce a plurality of beamformed streams of symbols, whereinthe beamforming matrix is based on a multiple path channel estimationfrom an RF receiver; and a plurality of inverse fast Fourier transformmodules operably coupled to convert the plurality of beamformed streamsof symbols from a frequency domain to a time domain to produce theplurality of streams of outbound baseband signals; modulation controlmodule operably coupled to determine the one of the plurality ofmodulation schemes indicated by each of the plurality of modulationcontrol signals based on the multiple path channel estimation from theRF receiver, wherein the modulation control module functions todetermine the plurality of modulation control signals by: determining asignal to noise ratio for each transmit path based on a correspondingportion of the multiple path channel estimation from the RF receiver; inresponse to the signal to noise ratio determined for each transmit path,determining a modulation scheme for each transmit path; and producingthe plurality of modulation control signals in response to themodulation scheme determined for each transmit path.
 8. The basebandtransmit processing module of claim 7, wherein the multiple path channelestimation from the RF receiver includes at least one of: a diagonalizedchannel (H) and a conjugate of a unitary beamforming matrix (V*).
 9. Thebaseband transmit processing module of claim 8, wherein the diagonalizedchannel (H) is based on eigen beamforming using singular valuedecomposition, wherein H=UDV*, such that y=Hx+n=UDV*x+n, where Ucorresponds to a unitary de-beamforming matrix, V corresponds to aunitary beamforming matrix, V* corresponds to the conjugate of theunitary beamforming matrix, y corresponds to the plurality of streams offrequency domain inbound baseband symbols, x corresponds to theplurality of streams of symbols, and n corresponds to noise, Dcorresponds to a diagonal matrix of D=[s₁ 0;0 s₂].
 10. The basebandtransmit processing module of claim 8, wherein the determining, for eachof the plurality of symbol mapping modules, a corresponding one of theplurality of modulation control signals comprises for a 2×N multipleinput multiple output (MIMO) wireless communication: setting z=Vx;determining a conjugate of the unitary de-beamforming matrix multipliedby the plurality of streams of frequency domain inbound baseband symbolssuch that U*y=U*UDV*Vz+U*n=Dz+N, where D corresponds to a diagonalmatrix of D=[s₁ 0;0 s₂] and N corresponds to a noise power and where s₁and s₂ represent first and second signal components; determining signalto noise ratio (SNR) for each transmit path of the MIMO wirelesscommunication, where SNR₁=s₁ ²/N₀, and SNR₂=s₂ ²/No, where the SNR₁represents the SNR for a first transmit path of the MIMO wirelesscommunication and the SNR₂ represents the SNR for a second transmit pathof the MIMO wireless communication; and determining the correspondingone of the plurality of modulated control signals based on at least oneof the SNR₁ and the SNR₂.
 11. The baseband transmit processing module ofclaim 10, wherein the determining the corresponding one of the pluralityof modulated control signals further comprises: determining a geometricmean for the SNR (SNRgeo) for each of the transmit paths of the MIMOwireless communication over subcarriers of an OFDM (orthogonal frequencydivision multiplex) frame of the MIMO wireless communication, whereSNRgeo=prod(1+SNRi)^(1/(N-1)); determining assigned bits (b) for theeach of the transmit paths based on an Aslanis formula, whereb=log₂(1+SNR/G), where G corresponds to margin such thatb₁<=log₂(1+SNRgeo₁/G₁) and b₂<=log₂(1+SNRgeo₂/G₂); and corresponding theassigned bits for the each of the transmit paths to a modulationconvention to produce the corresponding one of the plurality ofmodulation control signals.
 12. The baseband transmit processing moduleof claim 11, wherein the corresponding the assigned bits for the each ofthe transmit paths to a modulation convention further comprises:limiting one of the assigned bits in accordance withb_(i)=floor(log₂(1+SNRgeo_(i)/G_(i))/2)*2 such that a maximum b_(i)includes 8 bits/tone/stream; setting margin (G) to 0 dB; and equating ab_(i) of 2 to a 4QAM (quadrature amplitude modulation) modulationconvention, a b_(i) of 4 to a 16 QAM modulation convention, a b_(i) of 6to a 64QAM modulation convention, and a b_(i) of 8 to a 256 QAMmodulation convention.
 13. A modulation control module comprises: atleast one processing module; and memory operably coupled to the at leastone processing module, wherein the memory stores operationalinstructions that causes the at least one processing module to:determine a multiple path channel estimation in response to an RFreceiver feedback signal; determine a unitary matrix for beamforming foreach transmit path of a multiple input multiple output (MIMO) wirelesscommunication based on the multiple path channel estimation; determine asignal to noise ratio for each transmit path of the multiple inputmultiple output (MIMO) wireless communication based on the unitarymatrix for beamforming; in response to the signal to noise ratiodetermined for each transmit path, determining a modulation scheme foreach transmit path; and determine, for each transmit path of themultiple input multiple output (MIMO) wireless communication, amodulation control signal based on the determined modulation scheme. 14.The modulation control module of claim 13, wherein the multiple pathchannel estimation includes at least one of: a diagonalized channel (H)and a conjugate of a unitary beamforming matrix (V*).
 15. The modulationcontrol module of claim 13, wherein the multiple path channel estimationcomprises a channel characterization (H), wherein H=UDV*, such thaty=Hx+n=UDV*x+n, where U corresponds to a unitary de-beamforming matrix,V corresponds to a unitary beamforming matrix, V* corresponds to aconjugate of the unitary beamforming matrix, y corresponds to aplurality of streams of received baseband symbols, x corresponds to theplurality of streams of transmitted baseband symbols, and n correspondsto noise, D corresponds to a diagonal matrix of D=[s₁ 0;0 s₂].
 16. Themodulation control module of claim 15, wherein the memory comprisesoperational instructions that cause the at least one processing moduleto determine, for each transmit path, the modulation control signal fora 2×N multiple input multiple output (MIMO) wireless communication by:setting z=Vx; determining a conjugate of the unitary de-beamformingmatrix multiplied by the plurality of streams of frequency domaininbound baseband symbols such that U*y=U*UDV*Vz+U*n=Dz+N, where Dcorresponds to a diagonal matrix of D=[s₁ 0;0 s₂] and N corresponds to anoise power and where s₁ and s₂ represent first and second signalcomponents; determining signal to noise ratio (SNR) for each transmitpath of the MIMO wireless communication, where SNR₁=s₁ ²/N₀, and SNR₂=s₂²/N₀, where the SNR₁ represents the SNR for a first transmit path of theMIMO wireless communication and the SNR₂ represents the SNR for a secondtransmit path of the MIMO wireless communication; and determining thecorresponding one of the plurality of modulated control signals based onat least one of the SNR₁ and the SNR₂.
 17. The modulation control moduleof claim 16, wherein the memory comprises operational instructions thatcause the processing module to determine the corresponding one of theplurality of modulated control signals by: determining a geometric meanfor the SNR (SNRgeo) for each of the transmit paths of the MIMO wirelesscommunication over subcarriers of an OFDM (orthogonal frequency divisionmultiplex) frame of the MIMO wireless communication, whereSNRgeo=prod(1+SNRi)^(1/(N-1)); determining assigned bits (b) for theeach of the transmit paths based on an Aslanis formula, whereb=log₂(1+SNR/G), where G corresponds to margin such thatb₁<=log₂(1+SNRgeo₁/G₁) and b₂<=log₂(1+SNRgeo₂/G₂); and corresponding theassigned bits for the each of the transmit paths to a modulationconvention to produce the corresponding one of the plurality ofmodulation control signals.
 18. The modulation control module of claim17, wherein the memory comprises operational instructions that cause theprocessing module to correspond the assigned bits for the each of thetransmit paths to a modulation convention further comprises: limitingone of the assigned bits in accordance withb_(i)=floor(log₂(1+SNRgeo_(i)/G_(i))/2)*2 such that a maximum b_(i)includes 8 bits/tone/stream; setting margin (G) to 0 dB; and equating ab_(i) of 2 to a 4QAM (quadrature amplitude modulation) modulationconvention, a b_(i) of 4 to a 16 QAM modulation convention, a b_(i) of 6to a 64QAM modulation convention, and a b_(i) of 8 to a 256 QAMmodulation convention.